Ion mobility spectrometry (IMS) is a technique for separating and identifying ions in gaseous phase based on their mobilities. For example, IMS can be employed to separate structural isomers and macromolecules that have different mobilities. IMS relies on applying a constant or a time-varying electric field to a mixture of ions. An ion having a larger mobility (or smaller collision cross section [CCS]) moves faster under the influence of the electric field compared to an ion with a smaller mobility (or larger CCS). By applying the electric field over a separation distance (e.g., in a drift tube) of an IMS device, ions from an ion mixture can be spatially separated based on their mobility. Because ions with different mobilities arrive at the end of the drift tube at different times (temporal separation), and they can be identified based on the time of detection by a detector at the end of the drift tube. Resolution of the mobility separation can be varied by changing the separation distance.
Mass spectrometry (MS) is an analytical technique that can separate a mixture of chemical species based on their mass-to-charge ratio. MS involves ionizing the mixture of chemical species followed by acceleration of the ion mixture in the presence of electric and/or magnetic fields. In some mass spectrometers, ions having the same mass-to-charge ratio undergo the same deflection. Ions with different mass-to-charge ratios can undergo different deflections, and can be identified based on the spatial location of detection by a detector (e.g., electron multiplier).
IMS combined with MS can generate an IMS-MS spectrum that can be used in a broad range of applications, including metabolomics, glycomics, and proteomics. IMS-MS ion separation can be performed by coupling an ion mobility spectrometer with a mass spectrometer. For example, an ion mobility spectrometer can first separate the ions based on their mobility. Ions having different mobilities can arrive at the mass spectrometer at different times, and are then separated based on their mass-to-charge ratio. An example of an IM spectrometer is a structures for lossless ion manipulations (SLIM) device that can generate an IMS spectrum with minimal ion loss.